The invention relates to a tool for binding objects, in particular cable harnesses, having a band and a lock which secures the band ends. It is often necessary to set the band tensioning within predetermined limits in order that, on the one hand, sufficient tensioning is achieved and, on the other hand, the object which is to be bound and the band are not subjected to excessively high loading. For this purpose, the tool is equipped with a band-tensioning-limiting device. In the case of a first tool type (EP-B 299 387; U.S. Pat. No. 5,915,425), the band-tensioning-limiting device is designed as a load balance in which the force acting in the band-tensioning device is compared with a reference force predetermined by a spring. If the force acting in the band-tensioning device exceeds the reference force, then the connection between the band-tensioning device and a band-gripping gripper is released. In the case of this tool type, the band-tensioning-measuring device is integrated mechanically in the band-tensioning-limiting device. The accuracy of the band-tensioning limitation is thus severely restricted. In addition, it is barely possible to set a band tensioning of predetermined magnitude. In the case of another type of tool (EP-B 733 549), the pressure in a pneumatic tensioning drive is compared, likewise via a type of load balance, with a reference force formed by an adjustable spring. The tensioning operation is terminated as soon as a set threshold has been reached. Although this achieves a higher level of accuracy than with the band-tensioning-limiting devices of purely mechanical construction, it is capable of improvement. The structural outlay is also comparatively high. If it is desired to determine the magnitude of the tensioning achieved, it is additionally necessary to provide an electronic pressure sensor with display device.
The disadvantages of the prior art are avoided according to the invention by the means of claim 1, and preferably by those of the subclaims.
Accordingly, a band-tensioning-measuring device which establishes the relationship between a lateral deflection of the band and the force necessary for this purpose is provided. An essential advantage of the invention is thus that the accuracy of the measurement is not impaired by design conditions which are predetermined in respect of limiting the band tensioning. A further important advantage is that the band tensioning is measured directly on the band itself. Electronic measurement also directly produces a display signal, which makes it possible to monitor the setting.
Deflection is to be understood as the band being guided, between a pair of band guides arranged on one side of said band, over a deflecting guide which is located on its other side and deflects the band in the direction of the side of the pair of band guides. The pair of band guides may be formed by guide parts which are provided in the tool anyway, for example by the lock mount, on the one hand, and the band-tensioning device, on the other hand. It is more expedient, however, for the pair of band guides to be provided separately, to be precise in a structural unit with the deflecting guide and preferably also the band-tensioning-measuring device, in order that the geometrical relationship defined by said structural unit itself, irrespective of other structural tolerances of the tool. It is highly advantageous here that the magnitude of the deflection can be very low, namely preferably smaller than a fifth, further preferably smaller than a tenth, and further preferably smaller than a twentieth, of the distance between the band guides. This presupposes that the deflecting guide is seated approximately centrally between the band guides. If it is arranged considerably more closely to one band guide than the other, the deflection should be correspondingly smaller. The advantage of the small deflection is that the band can be pushed through more or less rectilinearly and the band-advancement means can thus be arranged in front (i.e. on the side on which the band-tensioning device is also located). This makes it possible to use the same drive elements for the band-advancement means and the band-tensioning device.
The band-tensioning-measuring device is expediently designed such that the force on the deflecting guide is measured with a given magnitude of deflection. Conversely, it is also possible, however, to measure the magnitude of the deflection with a given deflecting force, the latter being determined, for example, by a spring. If an electronic measuring element is used as a band-tensioning-measuring device, the measuring distance is so small as to be more or less negligible. Moreover, in conjunction with the band-tensioning-measuring device being designed together with the band guide and deflecting guide as an independent structural unit, this has the advantage that said structural unit can be exchanged in its entirety for replacement or maintenance purposes. It may also be treated as an optional element, it being possible for one and the same tool type to be supplied with or without a band-tensioning-measuring device or it easily being possible for a tool supplied without a band-tensioning-measuring device to be retrofitted with such a device.
In one embodiment of the tool, the band-tensioning device is provided with an adjustable band-tensioning-limiting device, and a device is provided for setting the band tensioning, said device, for its part, being influenced by the band-tensioning-measuring device. The arrangement may be such that, during each binding operation, the band tensioning which is actually achieved and established by the band-tensioning-measuring device is compared with a stored desired value. If deviations are established outside a certain tolerance range, the band-tensioning-limiting device is adjusted correspondingly.
In another embodiment of the tool according to the invention, the band-tensioning device contains a device for terminating the tensioning operation, this device being controlled directly by the band-tensioning-measuring device. It is possible to provide, for example, an electric clutch which is opened whenever the band-tensioning-measuring device signals that a predetermined band tensioning has been achieved.